Fourth-generation synchrotron radiation (SR) sources offer dramatically enhanced coherence, pushing the requirements for beamline stability to new extremes, particularly in spatial resolution for imaging, temporal resolution for dynamic studies, and X-ray nanoprobes. Therefore, the beamline must possess high stability while effectively propagating coherent photons during optical design. For fourth-generation SR sources with significantly enhanced coherence, wave-optics simulations must be incorporated into optical design processes. Here, we present the development of a vibration mode propagation (VMP) method for beamline vibration simulation. By utilizing vibration modes instead of wavefront vibrations and propagating them through the method developed in this work, the VMP method enables computational speeds up to 40 times faster than the brute-force method in actual beamline models of fourth-generation SR sources, and high-efficiency, fully wave-optics simulation of vibration is achieved. Furthermore, by integrating the VMP method with coherent mode decomposition, we extend its application to partially coherent SR beams, enabling a comprehensive analysis of vibration decoherence, position vibration, and the vibration impact of experimental sampling frequency.

A metrology method dedicated to position monitoring and correction for the ptychography setup at the High Energy Photon Source (HEPS, Beijing, China) beamline ID09 is proposed. The sophisticated design of the Invar interferometer metrology frame ensures optimal performance within the compact environment between the focal spot and the sample setup. The measurement method and error analysis are described in detail. The sample setup achieves a positional stability of less than 2 nm RMS from 1 Hz to 500 Hz. The 12.3 nm reconstruction resolution of 2D ptychography at 12.4 keV demonstrates that the interferometer metrology strategy is available.

The advent of fourth-generation synchrotron radiation sources has enabled advanced coherent X-ray techniques. However, high-flux pink-beam operation introduces significant computational challenges for wave-optics-based coherence analysis. Conventional approaches, such as Monte Carlo sampling of the electron beam or direct diagonalization of the cross-spectral density, become computationally prohibitive when extended to broadband spectra. In this work, we develop an integrated computational framework that combines Monte Carlo brightness convolution for efficient wavefront matrix construction, hierarchical incremental singular value decomposition to overcome memory bottlenecks in coherent mode decomposition, and spectral-spatial decomposition to extract a global orthogonal basis for rapid broadband propagation. The reliability of the proposed method is validated through comparison with Synchrotron Radiation Workshop (SRW) simulations and experimental measurements performed at the HEPS Hard X-ray Coherent Scattering (HXCS) beamline. Furthermore, the framework is applied to analyze chromatic aberrations in compound refractive lens focusing systems, quantitatively evaluating focal-spot broadening and coherence degradation inherent to pink-beam operation. The proposed framework provides a practical and scalable tool for the design and optimization of high-flux pink-beam coherent experiments at modern synchrotron facilities.

In situ x-ray mirror surface figure metrology under vacuum and high heat loads is essential for monitoring deformations and enabling adaptive corrections. This study introduces a high-precision vacuum metrology system based on a pentaprism long trace profiler, designed to monitor clamping and thermal deformations while enabling adaptive wavefront corrections. The pentaprism and scanning stage are vacuum-internal, with an external detector to minimize window errors. Two different optical configurations were studied: the Internal Optical Path with External Detector (IOP-ED) configuration and the external optical head configuration. Vacuum evaluations improved to sub-0.1 μrad RMS slope repeatability, yielding 0.23 μrad RMS systematic errors for the IOP-ED configuration, with a scan range of 150 mm on a flat mirror at a vacuum level of 200 Pa. Future enhancements include full-vacuum integration to eliminate residual instabilities.

Abstract The construction of the pink-beam small-angle X-ray scattering (SAXS) beamline, ID08, was completed at the High Energy Photon Source (HEPS) in 2025. To enable fast time-resolved scattering experiments, the ID08 beamline employs a pink X-ray beam as the fundamental photon source, which is emitted from an in-air planar undulator. The pink-beam exhibits an energy resolution of 0.95%, with a photon flux up to 3.2 × 1015 phs/s/0.1%bw@12 keV@200 mA and an energy coverage of 8–12 keV. The beam size at the sample position can be varied from 0.2 mm × 0.2 mm to 0.5 mm × 0.5 mm (H×V) using the primary slits. With the current beamline layout, the accessible q-range for SAXS measurement is 0.0105–6.68 nm–1, corresponding to a detectable particle size range of 1–600 nm. Coupled with three advanced pixel-array detectors and optical components installed at a later stage, such as compound refractive lens (CRL), this beamline enables not only millisecond-level time-resolved individual SAXS, wide-angle X-ray scattering (WAXS), and ultrasmall-angle X-ray scattering (USAXS) experiments but also simultaneous combined WAXS/SAXS/USAXS measurement. The HEPS-ID08 beamline supports both static and dynamic characterization of various material systems across length scales from angstrom down to submicron, opening up new avenues for structural investigations into non-equilibrium and time-dependent processes in materials.

The High Energy Photon Source (HEPS) is the first fourth-generation synchrotron radiation light source project in Asia, with an electron energy of 6 GeV, a circumference of 1360 m and a natural emittance of a few tens of picometers. As a green-field light source, the HEPS construction started in 2019 and is scheduled to be completed in 2025. Now civil construction, component fabrication and tunnel installation have been complected, and multipole milestones have been achieved in commissioning of the accelerator and beamlines. In this review paper, the design as well as the commissioning progress of the HEPS accelerator and beamlines are reported, where the challenges faced and corresponding measures during the design and commissioning are introduced.

Low-noise and high-stability constant-current drivers are critical components in precision electronic and optoelectronic systems, as current fluctuations directly limit the achievable system performance. This work presents a low-noise constant-current driver based on a current-sensing architecture combined with a parameters adjustable closed-loop control scheme, enabling effective suppression of current noise over a wide frequency range. The electrical performance of the proposed driver is first characterized at the circuit level. At an output current of 300 mA, a current noise spectral density of 15.22 nA root Hz @ 1 kHz is achieved, corresponding to an integrated RMS current noise of 942.88 nA over the 1 Hz-1 MHz bandwidth and a relative current fluctuation of 4.6 ppm. To further evaluate system-level performance, the driver is tested using a laser-based load, where current-induced noise is converted into measurable phase and frequency fluctuations through optical beat-note operation.The experimental results demonstrate that this design effectively suppresses current-induced noise and improves system stability. Owing to its low noise performance, this design provides a practical solution for precision electronic and optoelectronic applications requiring low-noise current power supply

Diamond is recognized as the ideal material for X-ray refractive optics in high thermal load and intense radiation environments, particularly for applications in fourth-generation synchrotron radiation and X-ray free-electron lasers (XFELs). However, the figure error and surface roughness of diamond refractive optics fabricated via laser ablation technology can significantly degrade their imaging and focusing performance. This work addresses key challenges associated with diamond lenses, including lens packing, step errors, surface roughness, and wavefront errors induced by figure error. In response to these issues, systematic optimizations and compensation strategies are proposed and validated. The results demonstrate a substantial improvement: the surface figure error of the single lens, as measured by X-ray speckle vector tracking (XSVT), is reduced to less than 1.5 mu m, the surface roughness is decreased by 74%, and the wavefront error is lowered by a factor of 2.38. These findings confirm that the optimized 2D diamond X-ray refractive focusing system, equipped with compensation techniques, exhibits superior imaging and focusing capability. This work thereby enhances the application potential of diamond refractive optics in next-generation synchrotron radiation sources and XFELs.

A novel aberration‐free X‐ray compound refractive kinoform lens design based on the Cartesian oval curve is presented, designated as the OVAL‐OK (OVAL Overlap Kinoform) lens. Material infilling of the kinoform step structure maintains focal spot dimensions while reducing focal intensity and reproducibility of structures. A SU‐8 OVAL‐OK lens fabricated through X‐ray lithography achieved vertical focal sizes of 70.8 nm (knife‐edge scanning) and 56 nm (wavefront propagation analysis) under 15 keV X‐ray illumination, using a 120 μm × 200 μm (horizontal × vertical) aperture and 40.8 mm working distance. The lens exhibits a horizontal structural depth of 170 μm and a minimum feature size of 5 μm. The observed discrepancy between direct knife‐edge measurements and wavefront‐derived values is attributable to the combined effects of geometric, diffraction, coherence, instrumental instability, etc. These results demonstrate the potential for achieving sub‐50 nm 2D focusing in future iterations through enhanced structural depth and expanded aperture dimensions.

Abstract A zone-plate-based full-field transmission X-ray microscopy (TXM) beamline has been successfully constructed and commissioned at ID30 of the High Energy Photon Source (HEPS). Based on extensive commissioning and optimization, the beamline now achieves the best spatial resolution of approximately 16 nm, which is derived from extrapolation of Fourier ring correlation (FRC) and radial power spectrum density (RPSD) analyses of imaging results of the Siemens star pattern whose finest directly resolved feature is 25 nm. This beamline is designed to provide full-field transmission imaging, absorption edge imaging, and X-ray absorption near-edge structure (XANES) imaging, revealing the 2D/3D distribution of structures, elements, and chemical valence states, respectively. To meet the stringent illumination requirements of zone-plate imaging, three key strategies were implemented: (i) selection of the red-shift radiation from the undulator source to obtain hollow-cone illumination by exploiting the ultralow emittance of the HEPS storage ring; (ii) a two-stage focusing scheme, comprising a toroidal mirror in the beamline and a beam-shaping condenser (BSC) at the end-station to achieve the illumination angle dictated by the numerical aperture of the zone plate; and (iii) a dedicated BSC design to provide a suitable imaging field of view (FOV) while delivering the required beam divergence magnification. Commissioning results confirm that the beamline specifications meet the design targets. The beamline’s capability for nanoscale structural imaging and XANES imaging is demonstrated through performance measurements and preliminary experiments, as presented in this work.

The stability and cooling performance of monochromators are critical factors determining the beam quality and productivity of synchrotron radiation beamlines. The existing monochromator at the 1W1B X-ray Absorption Fine Structure (XAFS) beamline of the Beijing Synchrotron Radiation Facility (BSRF) is now facing problems such as wear, flux drift, and reduced cooling efficiency after more than two decades of operation. Furthermore, the upcoming beam current upgrade to 900 mA makes a system capable of handling increased heat loads while maintaining high stability necessary. This study aims to develop a new water-cooled, vertical deflecting Double Crystal Monochromator (DCM) that achieves exceptional angular stability and effective cooling. The design focuses on eliminating vibration sources commonly associated with cooling water. A novel gravity-fed water-cooling system was implemented to isolate the monochromator from pump-induced vibrations. The mechanical design was optimized by reducing adjustable degrees of freedom to enhance rigidity, and cooling pipes were routed through the Bragg axis to minimize vibration transmission. Stability was evaluated using a high-precision three-axis laser interferometer (sampling at 1 kHz) under various flow rates and Bragg angles. Numerical simulations, online rocking curve measurement and Cu XAFS scanning confirmed effective cooling. Flow tests confirmed a cooling capacity suitable for the upgraded heat load. Stability measurements demonstrated an average relative pitch stability of 3.0 nrad RMS and roll stability of 10.1 nrad RMS (0.5–500 Hz) with a cooling flow rate of 1.5 L/min in long term. The best recorded long-term pitch stability was 1.8 nrad RMS. Power Spectral Density (PSD) and Cumulative Power Spectrum (CPS) analysis confirmed the effective isolation of characteristic pump frequencies in the pitch vibration spectrum. The combination of a high-rigidity mechanical design and a gravity-fed cooling system successfully achieves few-nanoradian stability, significantly exceeding typical performance for water-cooled instruments. This passive cooling approach offers a cost-effective and highly stable solution for sensitive optical components in synchrotron radiation facilities.

Accurate and efficient wave-optics simulation of partially coherent light transport systems is critical for the design of advanced optical systems, ranging from computational lithography to diffraction-limited storage rings (DLSR). However, traditional approaches based on Coherent Mode Decomposition suffer from high computational costs due to the propagating massive sets of two-dimensional modes. In this paper, we propose the Coherent Mode Decoupling (CMDC) algorithm, a high-throughput computational framework designed to accelerate these simulations by orders of magnitude without compromising physical fidelity. The method factorizes 2D modes into efficient one-dimensional (1D) components, while crucially incorporating a subspace compression strategy to capture non-separable coupling effects. We demonstrated the generality and robustness of this framework in applications ranging from computational lithography to coherent beamlines of DLSR.

Based on paraxial optics and the Takagi-Taupin theory, we establish an analytical framework for cylindrically bent Laue crystals that treats them as bulk diffraction devices and decomposes their behavior into geometric, kinematical, and higher-order scattering contributions. In this framework, we derive three fundamental results: a conservation relation accounting for aperture effects, a monochromatic focusing condition, and a polychromatic focusing condition. We further clarify the origin and limitations of common focusing conditions derived from geometric-optics arguments. These results deepen the fundamental understanding of bent Laue crystals and reshape their design logic, paving the way for practical applications.

The first water-cooling nano multilayer Kirkpatrick-Baez mirror system in the Structural Dynamics beamline (ID23) at High Energy Photon Source (HEPS) has been implemented. An Invar gantry is engineered to achieve a balance between light weight and stability. The cooling system, including eutectic gallium-indium (eGaIn), copper braids and a cooling water circuit with a multi-bend copper pipe in a compact space, decouples movement and mitigates vibration. The mirror cooling holders introduce less than 0.5 nm RMS height error and 0.1 µrad RMS slope error in the mirror surface shapes. A series of stability tests is applied to verify the mechanism structure. In a 1 h test assessment using a water-cooling flow of 4.5 L min-1, the system demonstrated a positional stability of 5.96 nm and an angular stability of 86.76 nrad from 1 Hz to 500 Hz. The focal spot size of 13.39 nm × 15.15 nm (H × V) at a photon energy of 21.8 keV demonstrates the system's performance.

After nearly 20 years of service, beamline 1W1A at the Beijing Synchrotron Radiation Facility undergoes an upgrade. To keep the beam spot to its designed specifi cations and to address the challenges posed by the increasement of the storage ring beam current, a newly designed bending mechanism for the monochromator is installed. The experimental setup includes updated equipment such as a 6-circle diff ractometer, a 2-dimensional array detector, a closed-cycle cryostat system, and a grazing incidence wide-angle X-ray scattering experiment system. Furthermore, the control system and user data management software were enhanced to support these hardware updates. These updates have provided the beamline with more flexible measurement modes and expanded the dimensionality of experimental data, allowing users to conduct in situ experiments over a wide range of sample temperatures. Benifiting from the upgrades, new experimental methods have become available, resultingin significant improvements in both efficiency and resolution.

Abstract The High Energy Photon Source (HEPS) is the first fourth-generation synchrotron radiation facility in China and Asia. As one of the 15 beamlines constructed at HEPS Phase Ι, the test beamline (ID42) is the world’s only test beamline equipped with both an undulator and a wiggler as insertion device sources, offering high brightness and coherence, a broad spectral range, a large beam size, and a high heat load. This paper presents the overall layout, optical design, key performance parameters, and pilot operation status of this beamline. By flexibly combining optical components such as a monochromator, filters, and compound refractive lenses (CRLs), the beamline supports multiple operation modes including white beam, pink beam, monochromatic beam, and focused beam. The monochromatic beam covers an energy range of 5–45 keV, while the white beam extends to energies beyond 300 keV. Depending on the operation mode, the beam size can be adjusted from the micrometer to the hundred-millimeter scale. With its flexible optical system and high-precision experimental platform, the test beamline accommodates the development and testing requirements of optical components and key equipment, providing essential support for the high-quality construction and stable operation of HEPS beamlines. It also offers a reliable experimental environment for detector development, X-ray optics research, and the exploration of synchrotron radiation techniques at fourth-generation synchrotron radiation facilities.

While 4D Gaussian Splatting (4DGS) has revolutionized high-fidelity dynamic reconstruction, safeguarding the intellectual property of these assets remains an open challenge. Conventional steganographic techniques often neglect the underlying kinematic manifolds, triggering non-physical artifacts such as severe temporal flickering and "FVD collapse". To address this, we propose 4D-GSW, a kinematic-aware watermarking framework designed to embed robust copyright information while preserving high spatio-temporal consistency. Unlike prior 4D steganography that primarily focuses on opacity-guided invisibility, our approach explicitly addresses the physical coherence of motion trajectories. We introduce a Spatio-Temporal Curvature (STC) metric to identify "Dynamic Instants," adaptively gating watermark gradient injection to shield critical motion manifolds from non-physical perturbations. To ensure global coherence across complex deformations, we formulate a joint HMM-MRF energy minimization model that synchronizes watermark phases within both temporal trajectories and spatial neighborhoods. Furthermore, an anisotropic gradient routing mechanism ensures that watermark embedding remains strictly decoupled from photometric reconstruction fidelity. Extensive experiments have demonstrated the superior performance of our method in robustly hiding watermarks while resisting various attacks and maintaining high rendering quality and spatiotemporal consistency.

Brilliance of the fourth-generation synchrotron radiation sources are increased in the order of magnitude, which further emphasizes the coherent applications. The zoom system of traditional optics can realize coherence regulation while achieving the target size of focus spots at designated position. This paper develops the design method of zoom system to fully exploit partially coherent fields. According to the first-order optics and imaging theory, the design method is reasonably simplified. The flux-optimization acceptance-angle ratio approximately linearly varies with the coherent fraction, which contributes to the slit-aperture determination. In order to validate the design method, wave-optics simulations are conducted in this paper.

The evolution from 3rd to 4th generation synchrotron radiation (SR) sources provide promising potential improvements in X-ray techniques, particularly in spatial resolution for imaging, temporal resolution for dynamic studies, and beam size control for nanoprobes. Achieving these enhancements demands effective vibration suppression in beamline systems. This challenge drives the need for optical designs that ensure efficient photon transport while maintaining vibration within acceptable thresholds. To address the advanced coherence requirements of fourth-generation SR sources, wave-optics simulations must be incorporated into optical design processes. We therefore propose a vibration mode propagation method using wave-optics techniques for beamline vibration simulation. Our approach achieves an almost 40-fold computational acceleration in actual beamline models compared to conventional methods, enabling direct analysis of propagating wavefront vibrations. This framework allows systematic evaluation of intensity distribution variations, coherence changes, and beam positioning errors caused by mechanical vibrations.